It's a bit late when you're already pregnant to figure out who is going to provide support. (Also: menstruation is another inequitable burden that is linked to reproductive capacity though not actual reproduction.)

So it's fine for there to be some cultural customs that give a bit of extra information in this regard in advance.

Anything can be done to excess, and we're also pretty good at compensating for a lack of something by finding alternatives, and it's possible to display chivalry disingenuously (incontrovertible signals are the most worthwhile), so it's not something to stress about overly much, I don't think.

But the behavior overall is fairly sensible.